Investigations on Cs-free alternatives for negative ion formation in a low pressure hydrogen discharge at ion source relevant parameters
| Autor: | Ursel Fantz, U. Kurutz, Roland Friedl |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2017 |
| Předmět: |
010302 applied physics
Materials science Hydrogen chemistry.chemical_element Diamond Context (language use) engineering.material Condensed Matter Physics 01 natural sciences 7. Clean energy Ion source Neutral beam injection 010305 fluids & plasmas Ion Nuclear Energy and Engineering chemistry Caesium 0103 physical sciences engineering Work function Atomic physics |
| Zdroj: | Plasma Physics and Controlled Fusion |
| ISSN: | 0029-5515 0022-3727 0963-0252 0953-8984 0741-3335 0094-243X |
| Popis: | Caesium (Cs) is applied in high power negative hydrogen ion sources to reduce a converter surface's work function and thus enabling an efficient negative ion surface formation. Inherent drawbacks with the usage of this reactive alkali metal motivate the search for Cs-free alternative materials for neutral beam injection systems in fusion research. In view of a future DEMOnstration power plant, a suitable material should provide a high negative ion formation efficiency and comply with the RAMI issues of the system: reliability, availability, maintainability, inspectability. Promising candidates, like low work function materials (molybdenum doped with lanthanum (MoLa) and LaB6), as well as different non-doped and boron-doped diamond samples were investigated in this context at identical and ion source relevant parameters at the laboratory experiment HOMER. Negative ion densities were measured above the samples by means of laser photodetachment and compared with two reference cases: pure negative ion volume formation with negative ion densities of about and the effect of H− surface production using an in situ caesiated stainless steel sample which yields 2.5 times higher densities. Compared to pure volume production, none of the diamond samples did exhibit a measurable increase in H− densities, while showing clear indications of plasma-induced erosion. In contrast, both MoLa and LaB6 produced systematically higher densities (MoLa: ×1.60; LaB6: ×1.43). The difference to caesiation can be attributed to the higher work functions of MoLa and LaB6 which are expected to be about 3 eV for both compared to 2.1 eV of a caesiated surface. |
| Databáze: | OpenAIRE |
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